Summary: Effect of co-phasing diversity on CDMA
downlink capacity
F. Tong, R.C. Atkinson, I. Glover, S.R. Pennock and
P.R. Shepherd
The impact of distributed antennas using co-phasing transmission diver-
sityon downlink CDMA channels is examined. An expression is derived
that demonstrates that uniform downlink signal-to-interference ratio
across users can be achieved by appropriately weighting the distribution
of transmit powers across distributed antennas. The capacity of a down-
link CDMA system employing distributed antennas with optimum
power allocation is then found by simulation.
Introduction: This Letter examines the impact of applying co-phasing
transmission techniques to distributed antennas. A distributed antenna
is an irregular array of antennas with large separation connected to
central processing via a range of technologies, e.g. radio over fibre [1].
It has previously been demonstrated that improved uplink signal-to-
interference ratio (SIR) is realised by distributed antennas compared to
a conventional (single) antenna [2]. This Letter considers the downlink.
In systems where multiple transmit antennas are used to transmit to
a single receive antenna, the output of each antenna must be time